What has happened to eight bridges along Interstate 89 in Vermont is like a piece of linoleum that has come loose from the floor. If somebody with gum on the bottom of their shoe walks across it, the linoleum pulls up.
A similar type of deterioration process has taken place over the past 40 years on several Vermont bridges, according to Gordy Eastman, superintendent of Winterset Inc., Lyndonville, VT. The company is overseeing the $9.5-million project to replace the bridges between Waterbury and Middlesex.
Before work began, crews removed the blacktop and discovered that what was supposed to be 2.5 in. of concrete had been worn down to less than half that amount. Since the 1960s, cars crossing the bridges have created vibrations that the pavement and concrete underneath it has simply deteriorated.
This was compounded by the fact that the brine formed when roads are salted every winter and then mixed with water has eaten away at the concrete. After being in the elements for so long, the naturally occurring solution has taken its toll. Even during the summertime when one would think the salt would be washed off by warm rains, salt and water join forces and continue to eat away at the road surfaces. It is similar to the pockmarks created when commercial salt is used over time to melt ice on cement sidewalks.
Between the two problems, the octet of bridges deteriorated to the point where they had to be replaced. The decks on each of them are being removed as well as the structural portions. Once the new parts are installed, contractors can pour the concrete.
Because concrete is a porous material, new additives are placed in it to fill all its pockets. Winterset is using both Super Plasticizer and Silica Fume as additives.
Super Plasticizer helps make the concrete more moist without having to add water to it, because water will make the concrete weaker. Silica Fume is a fine powder that fills all the voids in the concrete. “It makes concrete impervious,” Eastman explained. “There will be no leakage through the deck.”
The additives have been used in New Hampshire for the past five years and in Vermont for two years. Winterset recently used them on a bridge in Hartford, VT, and it worked well. The only problem is that it is “finicky,” Eastman said, “because if it isn’t cured well, it will crack. It is also twice as expensive as regular concrete.”
Throughout the project, Winterset will be responsible for numerous tasks. It will demolish the bridge decks, replace the steel beams, and repair sections of concrete on the bridge piers that have become chipped. The new concrete decks and asphalt overlays also will be created by Winterset.
The new pavement on the bridges will be a much higher grade than when they were first built. That’s because a membrane of asphaltic rubber will be placed in between the concrete and the pavement. The membrane, which will be installed by A.D. Rossi of St. Johnsbury, VT, will be bonded to the concrete and the pavement melted to the membrane.
“There will be a good bond between the three. Water will not go through,” Eastman explained. “Forty years ago, we didn’t have the technology we do today.” He added that the membrane was first used in Vermont only about two or three years ago. “We’re experimenting with new products all the time.”
Other subcontractors on the project include: F.R. Lafayette, guardrails and Scott’s Line Striping, both of Essex Junction, VT; Pike Industries of Burlington, VT, paving; and Ralph Derrah of St. Johnsbury, sheer studs.
Plenty of equipment is being used on the project, such as Link-Belt cranes and Caterpillar bucket loaders and forklifts. Link-Belt’s 25-, 50-, 80- and 100-ton cranes have all been utilized, along with the Caterpillar IT28 and 420, and a Teledyne TB825X hydraulic hammer on a Liebherr 912 excavator.
Although work on the bridges in the southbound lane didn’t actually start until April 2001, four crossovers, for each pair of bridges, were built last fall. Three of the pairs are located in Waterbury with the other one in Middlesex. They measure anywhere in length from 100 to 300 ft. (30 to 91 m). In all, 12,000 ft. (3,658 m) of highway will be closed in Waterbury and 5,000 (1,524 m) in Middlesex. Work will conclude in 2002, with bridges in the northbound barrel.
One of the challenges of the project is that construction crews can’t access the project from the interstate itself. They can get to it only from U.S. Route 2 which shadows I-89. Eastman has discovered that it is quite difficult to maneuver in between the neighboring bridges, which may be just 30 or 40 ft. (9 to 12.2 m) from each other. It is especially difficult when trying to swing any of the long beams into place.
“You have to limit the footprint of disturbance, and that will increase the cost,” Eastman said.
Many of the beams are still in decent shape so they can be salvaged for use in other bridge projects. Enough beams will be saved to build 18 other bridges each 100 ft. (30 m) long. But when they are removed from these spans, they have to be taken to a state facility where lead paint is sand blasted off them. It is a surprisingly expensive proposition. Eastman explained that it costs less money to purchase new beams than to remove the paint.
Likewise, new products such as Ice Ban melt ice from roads without causing damage, Eastman said, but it is quite expensive. Using the residue of wet-milled corn and the production of alcohol it freezes at a lower temperature than salt and is less corrosive than water. CEG
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